Create another database source

Because that some of the SQL could be slow, like the statistics of the countries, so we need use `Session` to connect to another database source , this source will run in front of a SQL cache (pgpool) so we can precache the result, to speed up

This repo is using the pgpool frontend: https://github.com/Greenstand/node-mapnik-1/blob/master/deployment/overlays/development/database-connection-sealed-secret.yaml

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